DESCRIPTION (adapted from the Abstract): Subtype E HIV occurs in South East Asia and has been found in both injection drug users (IVDUs) and commercial sex workers (CSWs) in central and south Vietnam. In Thailand, Subtypes E and B coexist: Subtype E predominates in heterosexual transmission whereas Subtype B is more common among IVDUs. This pattern is changing, with Subtype E now accounting for two thirds of new infections among Thai IVDUs. Recently, concurrent infections with two different subtypes of HIV and infection with virus that is a recombinant of two subtypes has been reported by several researchers. Sexual mixing of IVDUs and CSWs in Vietnam may have resulted in dual and/or recombinant HIV infection. In this application, the Investigator proposes to look for dual and/or recombinant HIV infection in IVDUs and their spouses in central and southern Vietnam--little HIV infection exists in northern Vietnam--and in CSWs in southwestern Vietnam along the Cambodian border. He and his research associates will also compare HIV subtypes occurring earlier in the epidemic with those occurring in both groups now and over the next three years. This study should provide insight into the shifting nature Type 1 human immunodeficiency viruses as the epidemic progresses in Vietnam and Southeast Asia, which should have import for vaccine development.